1. Field of the Invention
This invention relates to a door for a vehicle.
2. Description of the Prior Art
The vehicle door has conventionally comprised outer and inner panels both formed of steel plates. Recently, doors formed of synthetic resin have been proposed to save weight and for design-related purposes.
For example, there is disclosed in Japanese Unexamined Utility Model Publication No. 56(1981)-124015 a plastic vehicle door comprising outer and inner panels integrally formed by blow molding.
However, such a plastic vehicle door comprising integrally molded outer and inner panels gives rise to various problems.
First, since the thermal expansion coefficient of synthetic resin is generally up to ten times as large as that of steel, normal operation of the windowpane sliding mechanism, the door lock device and the like incorporated in the door can be prevented due to thermal expansion or thermal shrinkage of the door panels. Further, due to differences between the mounting structure on the synthetic resin door panel and the mounting structure on the steel door panel, various parts which have been used in the conventional steel door cannot be used in the synthetic resin door.
Second, since synthetic resin material is generally weaker than steel in strength and rigidity, steel reinforcements must be incorporated in the synthetic resin door in order to obtain sufficient rigidity of the door panels or to reinforce parts which must bear a local heavy load, because if the wall thickness of the synthetic resin door panels is increased instead, use of such synthetic resin door contributes little to weight-saving. Therefore, the conventional synthetic resin door cannot simplify the manufacturing process of the door.
Third, since, in the case of the integrally-molded synthetic resin door, even a slight change in the body line of the vehicle body affects the whole door, the integrally-molded synthetic resin door is disadvantageous with respect to developing variants of the body style.
Fourth, it is difficult to improve the workability of the door, since various parts must be mounted through the space between the inner and outer panels.